[AFFA]

I am going to prepare a Grignard reagent from 2-chloropropane in THF. Although the overall reaction is slightly exothermic, I still find it difficult to confirm that the initiation of Mg is done or not. I also tried adding a little 1,2-dibromoethane as additive and heat the solution up for a while. I am still not sure about the question stated above (initiation is done or not)? So, is there any definitive observation or chemical test for a successful initiation???   Thanks a lot

[Yggdrasil]

The initiation of the reaction should be fairly obvious to detect because most Grignard reagents are only partially soluble in ether, so the solution turns cloudy upon initiation.  Here's a webpage with some pictures showing how to tell whether the reaction has initiated:

http://www.chem.ucla.edu/~bacher/General/30CL/Grignard_rxn/initiation_of_rxn.html

[AFFA]

I see. Thanks  

[movies]

Alternatively, you could take out a small aliquot, quench it, and take an NMR.  Might not be so easy with propane as a byproduct though.

By the way, this is going to be a difficult Grignard reagent because you will get a lot of elimination products where the propyl Grignard acts as a base to effect an E2 elimination on 1-chloropropane to give propane and propene.